We study the electrophysiology of single retinal neurons, intracellularly, and stain the cells through the electrode with horseradish peroxidase (HRP) so that the synaptic connections of physiologically identified neurons can be identified with the electron microscope. AII amacrine cells, which are prominent among several types of amacrine cells intervening between rod bipolar cells and ganglion cells in the cat retina, quicken the initial sluggish rod waveform providing a faster rod response. Using Golgi impregnation, a new class of retinal neuron, has been identified in rhesus monkey retina. These cells are termed biplexiform cells since they arborize in both plexiform layers. Golgi-EM shows that in the outer plexiform layer (OPL) they form central elements at rod spherules, while in the inner plexiform layer (IPL) they are postsynaptic to rod bipolar cell axon terminals. Electron microscopy of excitatory, cholinergic synapses demonstrates interactions between synaptic vesicles and the presynaptic membrane. Release of transmitter is accompanied by selective depletion of synaptic vesicles aligned at the active zone, loss of half of the synaptic vesicles in the terminal, and synaptic vesicle openings at active zone.